1. The problem statement, all variables and given/known data http://imageshack.us/photo/my-images/855/10544781.png/ 2. Relevant equations a=[r''-r0'^2]er+[r0'' + 2r'0']e0 where 0 = theta 3. The attempt at a solution stumped about it, i've tried setting the above to 0 then work out r which is 200 m but that's just cluelessly subbing values into the equation, any directions as to where to head? thanks!